The present invention relates to variable displacement pumps for use in automatic transmissions.
A hydraulic system for a transmission pressurizes and distributes transmission fluid to the operating devices and to the lubrication and cooling circuits. A variable displacement vane type pump is often selected for the transmission pump. It employs a rotor and a slide with multiple vanes to vary the volume of fluid delivered to the hydraulic circuits. The slide is eccentrically offset from the rotor to create fluid chambers defined by the vanes, rotor, and inner surface of the slide. A compression spring positions the slide to create large fluid chambers as the default. When the transmission requires less volume of fluid by the pump, a pressure regulator directs fluid from the pump output line to a regulating chamber in the pump. Pressure in the regulating chamber pivots the slide against the force of the spring to more closely align the centers of the rotor and slide, thereby reducing the size of the fluid chambers. This reduces the amount of fluid drawn into the pump from the fluid reservoir and likewise, the amount of fluid output by the pump.
With variable displacement vane type pumps, it is desirable to minimize leakage from various sources into the regulating chamber as this is a root cause of line pressure instability. If excess fluid accumulates in the regulating chamber, then the pump outputs less fluid than is required by the transmission. For example, oil may leak from the fluid chambers, between the slide and an adjacent cover or housing, to the regulating chamber. Leaking to the regulating chamber may be reduced, but not eliminated, by higher performing seals and by tighter manufacturing tolerances to reduce clearances.
There are two ways to control pump output. The first and preferred way is to direct line pressure to the regulating chamber via the pressure regulator to decrease pump output. The second way is to remove pressure from the regulating chamber via the pressure regulator by exhausting fluid to increase pump output. It is believed that the pump operates in this mode due to excess fluid leaking to the regulating chamber. This second mode may result in shudder during shifts and an undesirable shift feel for customers.
A variable displacement vane type pump having features to minimize fluid leakage to the regulating chamber is needed.
The present invention is for a variable displacement vane type pump, which comprises a pump body having inlet and outlet ports, a rotor driven by a drive shaft and co-axially aligned therewith, a plurality of radially extending vanes slidably disposed in the rotor, and a slide pivotally disposed on a pivot in the pump body and having a central axis eccentric to the axis of the rotor. A plurality of fluid chambers are defined by the rotor, vanes, and slide which transfer fluid from the inlet to the outlet port. To vary the size of the fluid chambers, a regulating chamber is pressurized by a pressure regulator to pivot the slide against the force of a spring. The regulating chamber is configured as a semi-circular cylinder intermediate the pump body and an outer surface of the slide.
Leakage to the regulating chamber tends to create line pressure instability, which has a direct influence on clutch apply and torque transfer affecting shift quality. Therefore to isolate the regulating chamber from leakage thereto, a slide channel is formed in a face of the slide to channel fluid leakage from the fluid chambers away from the regulating chamber. The slide channel diverts any leakage from the pump fluid chambers to a non-regulating chamber through a port in the slide. A slide channel may be included on one or both sides of the slide.
Where the pump and pressure regulator are incorporated in the pump body, high pressure routings in the body may leak fluid to the regulating chamber. To divert such fluid before it reaches the regulating chamber, a housing exhaust channel may be formed in the pump body.